What is Penstock in a Hydropower Project?
A penstock is a steeply sloping pipe that carries water at high pressure from surge tank or a forebay to the turbine. It is designed to operate under very high head of water with least possible head loss. A penstock pipe experiences heavy stress and vibration due to the effect of water hammer during sudden closure of valve that control flow to the turbine. Anchor blocks and support piers are provided along the span of the penstock pipe in order to held it firmly in its position. Expansion joints are provided in case of long penstock pipes so as to avoid the forces due to thermal expansion and contraction. These joints are usually placed immediately downstream of an anchor block. A penstock pipe may have vertical and horizontal bends as per the project needs. It may have bifurcation or trifurcation before it enters into the powerhouse so as to feed the different turbine units. The major and minor head loss in penstock pipe can be determined as explained in pipe flow literature. A penstock pipe may be of following types:
- Exposed Penstock
- Embedded Penstock
- Buried Penstock
A penstock pipe in hydropower plant serves following different functions:
- To convey water from surge tank to the turbines with minimum loss of head
- To withstand the effect of water hammer during sudden closure of valve
What is Economical Diameter of Penstock?
The economic diameter of penstock is a diameter which minimizes the sum of annual cost of penstock pipe and annual value of power loss due to loss of head in the penstock pipe. The diameter of penstock pipe can be optimized either by analytical method or by graphical method so as to obtain the economical diameter of pipe.